Gene Hackman was airlifted to a trauma hospital in Florida today .. after the actor was hit by a car while riding his bike in the Florida Keys ... TMZ has learned.

The Florida Highway Patrol tells TMZ ... the 81-year-old Academy Award winner suffered injuries to his head and body.

We're told the accident took place around 3:00 PM local time.

The Florida Highway Patrol is conducting an investigation into the cause of the crash.

We're told Hackman is currently in stable condition.